Evaluating and Explaining Climate Science

An Inconvenient Temperature Graph

If your library has a copy of the 1991 IPPC First Assessment Report, you should take a look at the section on historical climate. It has a graph of temperature reconstruction for the last 1,000 years or so. It corresponds to what you find in every other standard work before 2000. Like this one:

Now take a look at the IPCC Third Assessment Report from 2001 (the “TAR”). In chapter 2, on page 134 you see this temperature reconstruction:

From IPCC Third Assessment Report

Whew! How did that happen?

It’s possible that this is science progress – new research uncovers new data and overturns old paradigms. Decades of work and hundreds of peer-reviewed papers did produce the consensus you see in the first graph. Maybe they were wrong.

This isn’t the place to write about the Hockey Stick debate, as its known. You can read about it for days – weeks even – and honestly, it’s probably worth every minute.

One place to start is with the Wegman report, one cherry-picked extract: “Overall, our committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.”

Edward J. Wegman analyzed the Mann et all 1998 paper – the paper upon which the IPCC based its new temperature reconstruction. But don’t take my cherry-picked word for it, read the whole thing for your yourself, make up your own mind.

And while we are on that subject, Wegman might well have great stature in the science community, but you have to judge for yourself, after all he’s not infallible. Other links for the hockey stick debate: the wonderful people at Real Climate, “Climate Science from Climate Scientists“; and Climate Audit (the link is a new mirror site, it just got overloaded due to popularity). Real Climate includes Michael Mann – no, not the director of Heat with Pacino and De Niro – he’s the author of the controversial 1998 paper that started the whole debate. And Climate Audit is run by Steve McIntyre, whose joint investigation with Ross McKitrick got the whole debate finally kicked into the hands of the NAS and Edward J. Wegman.

The history of our climate has a huge impact on the science of climate.

Here’s a climate reconstruction of the last 1,000,000 years:

From "Holmes' Principles of Physical Geology" 4th Ed. 1993

And a focus on the last 150,000 years from the same work:

Here’s a comment from this reference work (Holmes) in respect of these reconstructions:

The recent past has known dramatic and fundamental changes of climate and environment which have affected the whole Earth, from the top of the highest mountains to the bottom of the deepest oceans. Morever, many of these changes have occurred at surprising speeds. Although the Earth’s environment may now be changing in response to human activities, even without them, rapid and dramatic changes in the environment would occur quite naturally.

(Emphasis added)

The earth’s recent history and its implications will be an important theme of this blog.

A note for those new to temperature history. Proper temperature measurement on a worldwide basis only goes back into the second half of the 19th century. And the longest temperature series (from Central England) only goes back to the mid 17th century. So all attempts to measure the past history of our climate rely on proxies. Temperature proxies include ice core data and tree rings. Proxies aren’t like perfect thermometers and the further you go back the more difficult the analysis becomes.

In the cause of science and the spirit of balance I think the IPCC should display the million year temperature reconstruction prominently in its next assessment report.

Hi! I’m new to your site – came to it from hot-topic.
The Wegman Report – nothing to do with the presigious NAS, everything to do with Sen Joe Barton and his CO2 producing friends. There’s good analysis at Deep Climate and subsequently, and earlier at Deltoid

Ian Love is correct that Wegman was NOT appointed by the NAS. Gerald R. North chaired the NAS panel. The Wegman report appears to have been prepared at the behest of certain members of Congress — it certainly was touted by them (see the links Ian provided). In any case, it had absolutely nothing to do with the NAS.

The real NAS report is available easily on the web, and is well worth reading:

I find this stuff fascinating personally… so it kinda sticks out that the glacial periods between this interglacial and last wasnt as severe as the ones during the previous 800k years.. And this interglacial is obviously longer lived than the previous… wild speculation follows;-) So what is the current theory for the reasons for this? has there been subsidence of the land bridge in the berring strait? Or is this the result o incremental continental drift? Too my simple mind the malkovich cycles dont seem to fit the bill, maybe for a interglacial, but not the last 150k and then not the previous 850k years.

Off-topic, I know, but your comment about the length of the recent inter-glacial has reminded me of an hypothesis of mine: since Homo Sapiens antedated the previous inter-glacial period, may be it’s only the current one’s length that has permitted our current proliferation and consequent technological state?

Yes, read the NAS report. Their comments essentially say that Mann’s reconstruction is probably very good for the last 400 years, and less certain further back.

If you look at the IPCC graph you’ve posted, you’ll see that the two std deviation grey blur widens noticeably just at the 400 year mark. In other words, the greater uncertainty before 1600 was in Mann ’98. I haven’t seen a lot written on the ——-ist side about all the caveats in Mann ’98.

I’m curious about the first graph you show. The arc for the MWP is a dashed line rather than a solid one. It’s … interpolated? Speculation? Did your source give a reason for its been dashed rather than solid? There must be a reason for it. My immediate reaction is that the author of the graph is showing us that this part of the graph is less reliably known than the rest.

It would be interesting if you’d post their explanation if you have the book available.

Also, as I commented, it’s possible that the new reconstructions are scientific progress

Oh, I think when the available data grows by orders of magnitude that indicates progress of some sort. Given the near-constant attack on modern reconstructions, I think the fact that only a few criticisms have stuck and that the major one – Wegman’s criticism of short-centered PCA – makes no material difference to the Mann ’98 results, odds are that results are robust.

You could blow up every paper written by Mann and there’d still be enough reconstructions around that give similar results to outfit a hockey team.

Your comment got trapped by the amazing spam filter for breach of etiquette. Check out the rules.

Interesting question on why the dashed line. There is no comment in Holmes. I wondered about it at the time I scanned it but it was the only geology book I had to hand. I’ve seen the same graph in a bunch of other ones, don’t think there were dashed lines.. we will never know.

Your assessment of the reasons for the dashes makes sense.

This isn’t the place to revive the hockey stick debate. Even if I understood principal component analysis well enough to write about it (I don’t) there are way too many websites that discuss it to a very high level.

More interesting for people to see the last million years, the last 150,000 years – not well-covered ground.

Newcomers to the climate debate are usually amazed.

I hope we can take a good look at what’s known and unknown about the twists and turns of the Eemian and our current interglacial..

Paleoclimate reconstructions didn’t stop with the 1999 Nature paper by Mann, Briffa, and Hughes. A major effort to broaden the proxies used to model past climates was published in the journal PNAS by Prof. Mann’s group in 2008.

The methodology of this paper has been nearly universally accepted in public by the majority of climate scientists, and has not been questioned in public by any who adhere to the current consensus thinking, to my knowledge.

In contrast, the paper’s methods have come under withering criticism by many commenters doing “blog science.”

The most readily understood problem is this: the Mann group used a set of four proxies from Lake Korttajarvi, Finland that cannot be calibrated to the instrumental temperature record, 1850-on, due to spurious signals over that time. The Mann et al method requires such calibration. Therefore the relationship that Mann’s group accomplished to the temperature record is a miscalibration. In fact, it so so bad that two of the four proxies are used in an upside-down orientation, such that the “warmer” signal in the data is added to the reconstruction as “colder”, and vice versa.

Mann et al. were challenged in PNAS on this point by McIntyre and McKitrick. In their Reply, Mann et al. dismissed McIntyre’s description as “bizarre” — but without addressing the substance of the challenge.

In my own view, the paper’s methods are so defective that its broad acceptance by the professional climatology community raises questions about the credibility of the entire proxy-based climate reconstruction enterprise. At least on the scale of many-hundreds to a-few-thousands of years.

An interesting subject, but then we get to: do most climate scientists accept it? if yes, do they accept it because it’s good? because they are gullible? because it fits the preconceived agenda? if no, why don’t they say so…

Then lots of questions about motives and morals, which is not a topic for this blog, and before long we will join so many other blogs.

I think other blogs cover the MBH98/99 subject so much more thoroughly..

Now, Eemian interglacial reconstructions.. there’s a subject for this blog.

I am a retired scientist and conservationist. There seems to be cult pervading science that does not accept debate, proof, peer review and uses the additional cult of personality attack to replace proof.

[…] example, the usually meticulous Science of Doom was, in my opinion, off the mark with his analysis of the development of the science here, skipping straight from the First to the Third Assessment […]

I realise I’m a bit late to be commenting on this post but just found something that’s particularly relevant…

If you have a look at the appendix in Jones et al. 2009 (“High-resolution palaeoclimatology of the last millennium: a review of current status and future prospects” The Holocene, 19, 3-49) they try to describe where the IPCC 1990 Fig. 7c comes from.

It seems that it was compiled from a series of publictions by H. H. Lamb and was only based on temperature records associated with Central England, so not global.

Further, Jones et al. point out that “At no place in any of the Lamb publications is there any discussion of an explicit calibration against instrumental data, just Lamb’s qualitative judgement and interpretation of what he refers to as the ‘evidence’”.

The plot was then dropped from the IPCC 1992 Supplementary Report because it was not up to scratch. In the 1995 IPCC report things got better (although the reconstruction only went back to 1400) and then by IPCC 2001 we have the “Hockey Stick”…

SoD, do you not make corrections to your posts, in this case regarding the sponsorship of the Wegman report? Note that the very first sentence of the report says who asked for it, i.e. Joe Barton and another Republican politician.

Re deep-time paleoclimate, the Eemian is certainly of interest, but I think that the Pliocene and Miocene intervals where climate was able to come to equilibrium while CO2 was at approximately current levels are of even greater interest, as is the rapid response of the ice sheets to climate forcing during the long cooling of the late Pliocene.

..do you not make corrections to your posts, in this case regarding the sponsorship of the Wegman report? Note that the very first sentence of the report says who asked for it, i.e. Joe Barton and another Republican politician.

I do try to correct my posts.

I’m less interested when the subject isn’t about the science.

However, until the time when I can get interested in who asked who directly & indirectly and who each person was actually hired by, and which political affiliations give the game away.. I have removed the NAS reference to Wegman.

“The Wegman panel was made up of three statisticians from three different universities, none of whom had any professional connection to paleoclimatology or the AGW debate. The North panel was made up of eleven paleoclimatologists and two statisticians, most of whom had been professionally connected to the IPCC or the Hockey Team, some of them closely connected.”

It also quotes a Mann e-mail message about the North panel’s provenance as follows:

“‘The panel is entirely legit[im]ate, and the report was requested by Sherwood Boehlert, who as you probably know has been very supportive of us in the whole Barton affair … The panel is solid. Gerry North should do a good job in chairing this, and the other members are all solid. Christy is the token skeptic, but there are many others to keep him in check. ‘”

I recently discovered your blog and I love it. It has renewed my faith about tone in the climate discussion. I really enjoy your commitment to the robust findings of the science and your ability to frame matters in context.

That said, I wanted to address one issue in this article. You say:

In the cause of science and the spirit of balance I think the IPCC should display the million year temperature reconstruction prominently in its next assessment report.

2) This last sentence (“Sharp-eyed observers…”) carries a lot of subtext and skirts dangerously close to questioning motives and academic honesty of the IPCC authors. In the spirit of your excellent etiquette standards, I would recommend striking it altogether.

Matt… skirts dangerously close to questioning motives and academic honesty of the IPCC authors.

Matt here skirts dangerously close to accepting the motives and academic honesty of IPCC authors.

The point is that being silent about motives is not being neutral – it is implicit acceptance. So why is the credulity implicit in the silence he urges, to be preferred to skepticism ? Surely science – all of it – is wedded to skepticism ?

So why is the credulity implicit in the silence he urges, to be preferred to skepticism ?

While I can’t speak for others – I read this particular blog precisely because its skeptical and takes nothing for granted. The “silence” you mention so suspiciously is probably due to the fact that most knowledgable people agree on the fundamentals and are looking at other things of interest.

The conspiracy/competency memes that you are apparently trying to promote are certainly not welcome here and you will find many other venues in the blogosphere interested in such rubbish . (SoD, I hope you don’t mind me being slightly impolite).

Lot of stuff there. However. In order to state how much the planet has warmed since 1850, one would have to know the temperature of 1850 and today, in equivalent terms. To say that science and technology and networks of 1850 knew the temperature of the planet in equal terms as today, is simple convenience not reality.

From 1850, 1880 types of data it also is clear that 75% of the warming took place between the years 1977 to 1998. The globe has warmed an additional 0.2 degrees since 1998. Not at all inline with the rate of CO2 emitted to the atmosphere and the rate for those previous 21 years.

The planet is current demonstrating that it can not seem to get any warming then the last 5 highest temperatures of 1998, 2005, 2010 and 20014. It needs more input, heat input. All the re-radiating CO2 and Water Vapor on the planet can not add heat it can only hold it back longer to warm the atmosphere. The rock (planet) itself has heat at its core and the magnetic shift we have seen since 1850…. well they needs to be more heat from some source other than burning fossil fuels.

If human-co2 is responsible for the noted warming, then the current temperature should be closer to 16.0 degrees C than the current 21st century-to-date average of 14.4 degrees C. Something of the AGW science must be missing.

When scientists use such data to prove the existence of unprecedented warming, these scientists do not merit the term scientist, regardless of how much they think they know. They don’t know. But they can show the “proof” that convinces them – its all they know, nothing more.

It follows also that for a scientist is going to claim they know how much C02 was in the Earth’s atmosphere in 1850 compared to today, they need to prove that frozen water that was once at the surface is now so many meters below other layers of ice, how an accurate account over all those years and that can not be done. To prove that, one would need an air sample at the time a given drop of water froze and is claimed to have sealed in the exact measure of CO2 in the atmosphere at that time and then that frozen water drop maintained that value without leakage or infusion.

The real science here about AGW or NGW or no GW, will be time. Time will tell the story, if the science is correct or if the science has it wrong.

The main reason science could have it wrong, is in your introduction. You are so sure you are right, you no longer look for any other evidence. Evidence and the possible science that could find something you did not and do currently accept. Your science and your unyielding belief in your science and your own self is not the only barrier to the fact of the matter.

Thank you for the amazing report, and good luck
We shall see in about 25 years.
AL

Al: We have known how to calibrate thermometers with boiling and freezing water since 1700. You correctly note that surface air temperature hasn’t always measured in exactly the same manner. About 1850, scientists realized that thermometers didn’t reliably measure AIR temperature unless the thermometer was shaded from the sun by a well-ventilated enclosure (called a Stevenson screen) located about 2 m above the ground. This methodology became standard world-wide before 1900. Measurement of temperature over or in the surface of the ocean was more problematic. No one taking measurements a century ago expected their data to be used to determine changes of 0.1 degC or less in mean global surface temperature, so the historical record is far from perfect. Modern measurements from space agree with the older methods where their records overlap. Recently a group of competent skeptics – partially funded by the Koch brothers – began reprocessing all of the available data, but their conclusions about warming have been similar to earlier work.

You can read about dating ice cores and see a picture of layers at the link below. Evidence that counting layer works comes from looking at the volcanic ash that was deposited in a particular layer; say from the eruptions of Krakatoa (1883), Tambora (1815) or even Vesuvius (79). Since there are chemical differences between the volcanic ash deposited (both nearby and around the world) by different volcanos, the ice layers deposited at the same time as a major eruption have a chemical fingerprint that makes it easy to date them. If you had counted 1804 layers between ash from Krakatoa and Vesuvius, you would have confidence in this technique. Similar ash from large pre-historic eruptions is found the same number of layers down in both Antarctica and Greenland. (If one goes down far enough, the layers flow and thin slowly from the weight of ice above and dating become more difficult.

The earth’s surface temperature is highly variable. Mean temperature in March where you live probably varies an average of 1.5 degC from year to year. When temperatures from all over the globe are averaged for a whole year, it isn’t surprising to see a change of 0.1 degC from year to year. Between 1996 and 1998, mean global temperature rose 0.3 degC (from a record El Nino) and fell 0.2 degC in 1999. Given this much natural variability, we don’t expect to see mean global temperature rise exactly 0.02 degC every year. The IPCC’s climate models suggest that natural variability means that there is a 28% of seeing no warming in any 5-year period, a 9% chance of seeing no warming in a 10-year period and about a 2% chance of seeing no warming over a 15-year period. So the IPCC’s models haven’t been looking very good lately. A variety of reasons for this modest discrepancy (about 0.3 degC of missing warming) have been suggested. As you say, we shall see what happens over the next 25 years.

However, no matter what does happen, scientists will not change their minds about whether increasing GHGs should increase temperature (all other factors being the same). Laboratory measurements have established beyond any doubt that increasing GHGs will reduce the rate at which heat from the sun escapes to space. The surface of the planet emits an average of 390 W/m2 of thermal IR, but the GHGs in our atmosphere already slow down the rate of heat loss to space by about 150 W/m2, making the planet much warmer than it would be otherwise. More GHG’s will cause slightly more slowing in the future. The AMOUNT of warming scientists predict for a doubling of CO2 might change. That warming might be disguised by more natural variability than currently expect. The sun’s output could drop or more volcanos could erupt. Ocean currents could change. All of these complications make the Earth a lousy location for understanding how CO2 interacts with the infrared radiation that cools our planet. These complications were a good reason why the IPCC should have been making less confident projections for the past two decades. If you wanted to understand more, you could begin here.